The standard electrode potential ( M 3 + / M 2 + ) for V ,   Cr ,   Mn & Co are - 0 . 26   V …

The ${\mathrm{E}}^{⊝}$ values for the redox couple (${\mathrm{M}}^{3+}/{\mathrm{M}}^{2+}$) shows that ${\mathrm{Mn}}^{2+}$ and ${\mathrm{Co}}^{2+}$ ions are the strongest oxidising agents in aqueous solution.

The ions ${\mathrm{Ti}}^{2+}, {\mathrm{V}}^{2+} \mathrm{and} {\mathrm{Cr}}^{2+}$ are strong reducing agents and will liberate hydrogen from a dilute acid.

So, the Correct answer is ${\mathrm{V}}^{2+} \mathrm{and} {\mathrm{Cr}}^{2+}$.